Drilled pile

ABSTRACT

A method of installing a pile  10  in a subsea substrate is provided, which method comprises the steps of providing a pile  10  with a drill bit  14  at one end, and rotating both the pile  10  and the drill bit  14  relative to a substrate to form a bore. Also provided is a subsea pile  10  in the form of an elongate member  12  with a drill bit  14  fixed at one end thereof. In certain embodiments, the elongate member  12  may be tubular, allowing fluids to be supplied to the drilling face via the pile. Such fluids may be drilling mud, sea water, or a settable material for fixing the pile in the bore.  
     In preferred embodiments of the invention an upper portion of the pile may be adapted to be laterally flexible.

DESCRIPTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a drilled pile, particularly foruse in subsea applications. The pile is suitable for use as a mooringtermination point or anchor on the seabed. The invention further relatesto a method of installing such a pile.

[0003] 2. Background to the Invention

[0004] A variety of pile systems and anchoring systems are known in theart; however, such systems suffer from a number of disadvantages.Conventional drilled piles either require the pre-drilling of a hole,removal of the drilling apparatus, and insertion of the pile; or areprovided as an integral pile\drilling member, with the drilling memberbeing removed from the pile after drilling. Either of these systems isrelatively costly and time-consuming to install.

[0005] Further, such conventional piles are constructed so as to beresistant to bending forces, as will be experienced by the pile onapplication of any non-axial loading. Accordingly, piles areconventionally formed of heavy rigid tubing of relatively largediameter; the relatively large diameter of the tubing is also useful intransferring lateral forces into the surrounding soil. At least in anintegral pile/drilling member, the large diameter of the pile alsofacilitates accommodation of the drilling member and associated drillingapparatus within the relatively large diameter pile bore. However,handling of such large diameter heavy piles is difficult and, moresignificantly, the drilling of a large diameter bore to accommodate thepile is time-consuming, and thus expensive.

[0006] It is among the objectives of embodiments of the presentinvention to obviate or alleviate these and other disadvantages of knownpiling systems.

SUMMARY OF THE INVENTION

[0007] According to a first aspect of the present invention, there isprovided a method of installing a pile in a subsea substrate, the methodcomprising the steps of:

[0008] providing a pile with a drill bit at an end thereof; and

[0009] rotating and advancing the pile and the drill bit relative to asubstrate to form a bore.

[0010] According to a second aspect of the present invention, there isprovided a subsea pile comprising an elongate member with a drill bitfixed at one end thereof.

[0011] The present invention provides an integral pile\drilling meanswhich may be used to drill a bore into which the pile advances as thebore is formed. Typically, the drill bit is not recovered, therebymaking the method fast and relatively inexpensive.

[0012] The pile and the drill bit are rotated together, thereby removingthe need for bearing arrangements to enable the drill bit to rotateseparately of the pile. In certain embodiments, the pile may comprise asection of conventional drill pipe, with a drill bit at an end thereof.As the pile is rotated as it is advanced through the drilled bore, thefriction between the bore wall and the pile is relatively low, incontrast to arrangements in which a pile is advanced into a drilled borewithout rotation.

[0013] Preferably, the pile is an elongate tubular member. This permitsfluids, such as drilling fluid or “mud”, to be supplied to the drill bitand drilling face via the pile. Other drilling fluids, including seawater, may be utilised; sea water offers the advantage that the fluidneed not be recovered, providing a considerable simplification in thepile drilling apparatus.

[0014] Preferably, the method further comprises the step of securing thepile in the bore. This may be achieved by passing a settable materialinto the bore, between the pile member and the bore wall, and allowingthe material to set in the bore. Conveniently, the settable material iscement, grout or the like, and will be delivered to the section of thebore which passes through the firmer soil formations which are generallyfound at depth below the surface soil layers. Use of the preferredtubular member to deliver a settable material downhole provides a simpleand efficient means to fix the pile in the bore. The absence of anyseparate drilling member within the pile of the present invention alsoavoids the risk of the drilling member being cemented within the pile.Alternatively, the pile may be cemented or grouted in the bore bydelivering cement via a separate arrangement of conduits and hoses, anda cement fill-up device may be used to divert slurry into cement hoses,which are directed into the bore externally of the pile.

[0015] In other embodiments of the invention it may be possible tosecure the pile in the bore by other means, for example by providingradially extending members on the pile. Of course, in some embodimentsthe soil formations may swell or collapse to grip the pile, or theintended function of the pile may not require the pile to withstandelevated axial loads, such that cementing or the provision of securingmembers is not required.

[0016] Preferably, at least an upper portion of the pile is adapted toflex in response to lateral loading. The pile may be formed of standardoilfield tubulars, such as drill pipe; drill pipe is designed forstraightforward and secure connection and has a low bending stiffnessbut high tensile strength and resistance to fatigue failure. Further,the resistance of the pile to lateral forces may be varied along itslength, such that the bending characteristics and bending radii of thepile may be controlled. For example, a lower portion of the pile may berelatively rigid, and may be grouted or cemented in the bore. Therelatively high rigidity may be achieved by using heavier section drillpipe, drill collars or even bore casing to form the pile. The pile maythus be adapted for specific applications, and particular soil and rockformations, as would be known to the pile installer from previoussurveys, knowledge or experience. A pile having such a flexible upperportion will withstand axial loads in a comparable manner to aconventional pile, but when subjected to lateral forces the upperportion of the pile will bend, and effectively translate the lateralforces to axial forces which are withstood by the lower portion of thepile. This enables the pile to be more versatile and durable thanlaterally rigid piles. Conventional piles may be installed withforce-dispersing collars, in order to transmit lateral forces andstresses away from the pile into the surrounding medium; sucharrangements are generally unnecessary with a laterally flexing pile.Conventional piles are also typically of large diameter, for similarreasons; the present invention enables piles to be made more slender. Aswell as reducing the bulk and expense of the pile, the provision of asmaller diameter pile facilitates drilling of the bore to accommodatethe pile; if the diameter of a pile in accordance with an embodiment ofthe invention is even only half the diameter of a correspondingconventional pile, the bore drilled to accommodate the pile is only onequarter of the area of the bore necessary to accommodate theconventional pile.

[0017] Preferably, the pile is provided with a mooring line connection.Most preferably, the mooring line connection includes a flexible memberwhich may be in the form of a wire rope, chain or the like. If a mooringline is not to be connected prior to installation of the pile, theflexible member may be secured to the body of the pile by cable ties orother restraining means; this avoids the risk of the connectionobstructing the installation of the pile. A portion of the connectionmay be buoyant, to facilitate location of the connection followinginstallation of the pile. Alternatively, a mooring line connection maybe rotatably mounted on the pile.

[0018] The pile and drill bit may be driven by connection to a drillstring or other elongate member. The drill string may be substantiallyconventional and preferably the connection between the string and thepile may be broken from surface once the pile is installed to thecorrect depth, such that the drill string may be retrieved.Conveniently, this may be achieved by an appropriate terminationassembly, for example, a low torque back-off disconnection system.Alternative termination assemblies as known in the art may also beutilised. Most preferably, the termination assembly is positioned at alevel relative to the substrate surface such that the pile, or a portionof the pile, does not have to be recovered once the pile is no longer inuse.

[0019] The drill string may extend to and be driven from surface, forexample by a rotary motor provided on an installation vessel.Alternatively, the pile may be driven by a motor, such as a conventional“downhole” motor, suspended from a drilling vessel on a drill string orsuspended from a barge or the like by a flexible member such as a craneline and coupled to a fluid supply by an appropriate hose. This latterarrangement allows the drilling operation to be carried out withoutrequiring the provision of a relatively expensive floating drillingunit, there being no requirement to provide rotary transmission fromsurface. It is envisage that the drive assembly may be coupled to somemeans of opposing reactive torque generated by the motor, which wouldotherwise tend to cause the assembly to rotate in the opposite directionto the desired direction of rotation of the drill bit. This could be aguide-frame located on the seabed, with a key way that interacts withanti-rotation keys on the assembly.

[0020] The drill bit may take any suitable form, depending on the soilconditions and other requirements, such as the bore length and diameter.As the drill bit is likely to be left in the bore with the pile, that isbe non-recoverable, the bit will therefore only be required to drill asingle relatively short bore and may therefore be of less robustconstruction, and therefore less expensive, than a conventional drillbit. The drill bit may be of conventional form or may be formedintegrally with the end of the pile, for example by welding, depositingor otherwise forming cutting structures on the end of the pile, such asblades provided with tungsten carbide aggregate thereon. Typically, thedrill bit will be of a diameter greater than the pile. Alternatively,the drill bit will be of smaller diameter than the pile, fluid erosionor applied weight being utilised to displace softer sediments toaccommodate the pile.

[0021] According to a further aspect of the present invention, there isprovided a pile comprising an elongate member with a drill bit at oneend thereof, wherein the pile has at least an upper portion adapted toflex in response to application of lateral loading thereto.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] These and other aspects of the present invention will now bedescribed, by way of example, only with reference to the accompanyingfigures, in which:

[0023]FIG. 1 shows a side elevation of a pile according to an embodimentof the present invention during the drilling phase of installation;

[0024]FIG. 2 shows the pile of FIG. 1 during the grouting phase;

[0025]FIG. 3 shows the pile of FIG. 1 during the disconnection of thedrill string;

[0026]FIG. 4 shows the pile of FIG. 1 during the connection of themooring line;

[0027]FIG. 5 shows the pile of FIG. 1 when connected to a mooring line;and

[0028]FIG. 6 shows a mooring line connection in accordance with afurther embodiment of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

[0029] FIGS. 1 to 5 of the drawings show a pile in accordance with anembodiment of the present invention. The pile 10 comprises a tubularelongate member 12, in this example formed predominately of standardjoints of drill pipe, with a rotary drill bit 14 connected to the lowerend of the member 12, in the illustrated example the diameter of thedrill bit 14 being greater than the member 12. A drill collar 16 isprovided at the lower end of the member 12 above the drill bit 14. Aconnection assembly 18 is provided at the upper end of the pile 10 andreleasably connects the pile 10 to a rotary drill string 20. The drillstring 20 extends to the surface and an appropriate installation vessel(not shown) provided with a motor for driving the string 20.

[0030] Also connected to the connection assembly 18 is a cable 22 at thefree end of which is a mooring line coupling 24. The other end of thecable 22 is coupled to the pile 10, the intermediate portion of thecable 22 being releasably secured to the drill string 20 by means of anumber of cable ties 26.

[0031] The installation of the pile 10 is carried out as follows. Thepile 10 and drill bit 14 are rotated together by means of the drillstring 20, and driven into the bore thereby generated in the seabed(FIG. 1). Cutting or drilling fluid is pumped from the surface throughstring 20 and the member 12 to the drill bit 14. The cutting fluidpasses from jetting nozzles in the bit 14, cooling the bit and washingcuttings away from the end of the bore. The cutting fluid and theentrained cuttings pass up between the member 12 and the bore wall todischarge into the sea.

[0032] In this example, the pile is driven to a depth where the end ofthe pile 10, marked by the connection assembly 18, is below the surfaceof the seabed, to ensure that the upper end of the pile does notconstitute a subsea obstruction which would have to be removed afteruse.

[0033] Once the pile has been drilled to the desired depth, as shown inFIG. 2, cement 28 is pumped down the drill string 20 from surface, andpasses through holes (not shown) in the pile 10 and drill bit 14, andinto the borehole surrounding the pile 10. The fill level of the cement28 may be determined as appropriate for the specific application andsoil conditions, and in this example it will be seen that the bottomhalf of the pile is cemented in the bore.

[0034] This section of the pile is located in firmer soil sediments,below the softer surface sediments.

[0035] Once the cement 28 has set, and the pile 10 is secured in thehole, the drill string 20 is disconnected from the pile 10 at theconnection assembly 18 (FIG. 3) by rotating the string 20counter-clockwise. The cable ties 26 break as the drill stay 20retracts, releasing the cable 22. The coupling 24 at the end of thecable 22 may be kept clear of the drilled hole and the seabed by meansof a buoyant attachment.

[0036] As shown in FIG. 4 a mooring line 30 is then connected to thecable 22. The mooring line 30 may be guided and connected by a remotelyoperated vehicle or by other means.

[0037]FIG. 5 illustrates the response of the pile 10 when subjected tolateral mooring line loads once the installation is complete; lateralforces applied via the mooring line 30 deflect the flexible upperportion of the pile 10 above the section secured with cement 28. Suchdeflection may be elastic or in some applications plastic, causingpermanent deformation of the pile. The deflection of the pile 10displaces some of the surrounding softer surface sediments 32 and causesthe lateral forces to be translated to axial forces which are resistedby the cemented lower portion of the pile.

[0038] Finally, FIGS. 6a and 6 b show cross-sections of a combinationdrill string disconnection\mooring line connection subassembly 118, inaccordance with a further embodiment of the present invention. In FIG.6a the upper drill string 120, used to support and rotate the pile 110during installation, is provided with a termination assembly 133 fortransferring torque from the drill string 120 to the pile 110, thestring termination assembly 133 including a male ratchet thread 135 forengaging a corresponding female thread. Disconnection of the drillstring 120 occurs at a releasable joint 134, which in this particularexample is a low torque left-hand back-off disconnection system orsafety joint.

[0039] The termination subassembly 118 includes a guide comprising afunnel 136 and a length of plastic pipe 138. This serves the function,shown in FIG. 6b, of aligning a mooring connection assembly 140 with thetermination assembly 133, and of course prevents the surrounding softsoil from covering the safety joint 134 after the withdrawal of thedrill string 120. The mooring connection assembly 140 comprises themooring line 130, a mooring line socket 140, and a male thread ratchetassembly 142.

[0040] It will be seen that the foregoing embodiments of the inventionprovide relatively simple and inexpensive alternatives to conventionalpiles and installation methods. In the preferred embodiment of thepresent invention, the provision of a flexible pile allows theorientation of the load applied to the pile to be controlled: underlateral loading the pile has a tendency to form an arc, substantiallyaligning the axis of the part of the pile subject to load with theorientation of that load. This also allows the bending stresses to berelatively evenly applied across a relatively long section of the pile,as opposed to the use of a stiff or inflexible pile which results in thebending stresses being concentrated in a small section of the pile. Apile in accordance with the preferred embodiments of the presentinvention might thus typically deflect under load by 5-80 degrees, asopposed to a 0.1 to 5 degree deflection of a conventional pile. Using aflexible pile, and omitting a separate drill string within the pile,allows use of piles in accordance with embodiments of the invention withan outside diameter (OD) typically 3-6 times less than a conventionalpile to provide similar load-bearing capabilities. For example, aconventional pile of 15-30″ OD may be replaced with a pile in accordancewith an embodiment of the invention formed of 5″ drillpipe.

[0041] Although the invention has been described primarily withreference to subsea applications, it will be understood by those ofskill in the art that the invention is not limited thereto.

What is claimed is:
 1. A method of installing a pile in a subseasubstrate, the method comprising the steps of: providing a pile with adrill bit at an end thereof; and rotating and advancing the pile and thedrill bit relative to a substrate to form a bore.
 2. The method of claim1, wherein the drill bit is not recovered.
 3. The method of claim 1,wherein the pile is an elongate tubular member and drilling fluid issupplied to the drill bit via the pile.
 4. The method of claim 1,further comprising the step of securing the pile in the bore.
 5. Themethod of claim 4, wherein the pile is secured in the bore by passing asettable material into the bore, between the pile member and the borewall, and allowing the material to set in the bore.
 6. The method ofclaim 5, wherein the settable material is delivered to the bore via aninternal bore in the pile.
 7. The method of claim 1, wherein the pile isat least partially formed from standard oilfield tubulars.
 8. The methodof claim 1, wherein the pile and drill bit are rotated by a drivenelongate member connected thereto.
 9. The method of claim 8, wherein theconnection between the elongate member and the pile is broken fromsurface once the pile is installed to the correct depth, such that theelongate member may be retrieved.
 10. The method of claim 9, wherein theconnection is positioned at a level relative to the substrate surfacesuch that the pile does not have to be recovered once the pile is nolonger in use.
 11. The method of claim 8, wherein the elongate memberextends to and is rotationally driven from surface.
 12. The method ofclaim 8, wherein the elongate member is rotationally driven by a motorpositioned below the surface of the water.
 13. A subsea pile comprisingan elongate member with a drill bit fixed at one end thereof.
 14. Thepile of claim 13, wherein the pile is an elongate tubular member. 15.The pile of claim 13, wherein at least an upper portion of the pile isadapted to flex one or both of elastically and plastically in responseto lateral loading.
 16. The pile of claim 13, wherein the pile comprisesstandard oilfield tubulars.
 17. The pile of claim 15, wherein theresistance of the pile to lateral forces varies along its length, suchthat the bending characteristics and bending radii of the pile may becontrolled.
 18. The pile of claim 17, wherein a lower portion of thepile is relatively rigid.
 19. The pile of claim 13, wherein a lowerportion of the pile is adapted to be grouted or cemented in the bore.20. The pile of claim 13, wherein a lower portion of the pile comprisesrelatively high rigidity members, including one or more of heavy sectiondrill pipe, drill collars and bore casing.
 21. The pile of claim 13,wherein an upper portion of the pile is adapted to bend when subjectedto lateral forces and translate the lateral forces to axial forces whichare substantially withstood by the lower portion of the pile.
 22. Thepile of claim 13, wherein the pile is provided with a mooring lineconnection.
 23. The pile of claim 22, wherein the mooring lineconnection includes a flexible member.
 24. The pile of claim 23, whereina portion of the connection is buoyant, to facilitate location of theconnection following installation of the pile.
 25. The pile of claim 13,in combination with an elongate member for extending to surface, and aconnection between the elongate member and the pile which is adapted tobe broken from surface once the pile is installed to the correct depth,such that the elongate member may be retrieved.
 26. The combination ofclaim 25, wherein the connection is a low torque back-off disconnectionsystem.
 27. The combination of claim 25, wherein the elongate member isadapted to be rotationally driven from surface.
 28. The combination ofclaim 25, further including a motor for location below the sea surface.29. A pile comprising an elongate member with a drill bit at one endthereof, wherein the pile has at least an upper portion adapted to flexin response to application of lateral loading thereto.